Whether open access operators are playing on a level playing field or not rather depends on how you look at it. They have both advantages and disadvantages over franchised operators. Some of the advantages being they don't have any (expensive) legacy staff or infrastructure (e.g. depots) and can carefully select the routes they want to operate. The main disadvantage is if they don't make a profit they go bust as they will not receive any form of subsidy. The DfT and the ORR both currently view OAO's quite favourably as they tend to run services at a lower cost than franchised operators, can provide services that franchised operators can't or won't and have been shown to grow the market.
One thing that certainly shouldn't happen is a total free for all and the ensuing chaos that occurred after bus deregulation with companies fighting each other over profitable routes and ditching unprofitable ones, which if replicated on the railway would leave the tax payer with a very large bill.
One thing that certainly shouldn't happen is a total free for all and the ensuing chaos that occurred after bus deregulation with companies fighting each other over profitable routes and ditching unprofitable ones, which if replicated on the railway would leave the tax payer with a very large bill.